Here’s my translation
Þegar Signý hafði aldr til, var hún gift þeim konungi, er Eirekr hét. Hann fell í vestrvíking.
As-soon-as Signý had age to (ie was old enough), she was given-in-marriage to that king, who was called Eirekr. He fell (in battle) in a feebooting-expedition-to-the-West
Dóttur áttu þau saman, þá er Hildr hét, ok var hún meyja fríðust.
Together they had a daughter, that-one (she) (<þá> = acc fem sg of <sá>) who was-called Hildr, and she was [the] most-beautiful of girls (fem gen pl).
Fór Signý þá til föður síns ok var með honum.
Signý went then to her father and was (stayed) with him.
Drottning fekk sótt, þá hana leiddi til bana, en konungr barst lítt af, en Signý var í skemmu ok hafði sorg mikla eptir konung sinn ok móður.
[The) queen got that sickness [which] (<þá> = acc fem sg of <sá>) led her to death, but (and) [the] king bore-himself poorly from [it] (ie he took it hard), but (and) Signý was (stayed) in a lady’s-bower and had much sorrow in-respect-of her king and mother.
Konungr fekk þá drottningu, er Grímhildr hét.
[The] king got (in marriage) that queen, who was-called Grímhildr.
Hún var fögr at sjá, en innan var hún it mesta flagð.
She was fair to behold, but from-within (ie beneath that fair exterior) she was the greatest ogress.
Konungr unni henni mikit.
[The] king loved her greatly.
Þau gátu at eiga sjau dætr, ok brá þeim öllum til móður sinnar ok urðu inar mestu flagðkonur.
They got to have seven daughters, and they all took after (lit: [it] shaped them all to, <e-m bregða til e-s>, Z9) their mother, and became the greatest ogresses.
Þat bar til í ríkinu við kvámu Grímhildar, at maðr hvarf hverja nótt, ok ætluðu allir, at Grímhildr mundi því valda.
That happened in the-kingdom with [the] coming of Grímhildr, that a person (man) disappeared every night, and all supposed, that Grímhildr would be-the-cause of that.
Konungr tók nú at eldast, ok þótti drottningu minna verða af hjáhvílum en hún vildi.
[The] king now started to grow-old, and [it] seemed to [the] queen to become less (<minna> = compar adv of <lítill>) of ‘beddings-with’ (cf <hvíla hjá e-m>, under <hjá>, Z1) (ie that ‘sleeping-with’ was becoming less, that she was getting less sex,) (see also <verða af e-u>, Z8) than she wanted.
Hugsar hún nú at svíkja konung ok fá sér annan ungan.
She contemplates now to deceive [the] king and to get for-herself another, a young [man]
Gefr hún honum nú eitr at drekka, ok fær hann þegar bana af, ok var hann heygðr hjá drottningu sinni.
She gives him now poison to drink, and he receives at-once death from [it], and he was buried (on a how) beside his queen.
Grímhildr illskaðist nú svá, at hún eyddi allt ríkit bæði af fé ok mönnum.
Grímhildr now grew- so -wroth-and-furious , that she laid-waste the-kingdom both of property and persons.
Eptir þessi verk Grímhildar gekk hún til skemmu þeirar, er Signý sat ok dóttir hennar, en er hún kemr þar, mælti hún svá: "Þú, Signý," segir hún, "hefir lengi í sæmd mikilli ok sælu setit, en ek skal þat allt af þér taka, ok þat legg ek á þik, at þú hverfir í burt ok byggir í helli ok verðir in mesta tröllkona.
After these deeds (neut plural) of Grímhildr, she went to that lady´s-bower where Signý sat (stayed) and her-daughter, but (and) when she comes there, she spoke so: “You, Signý,” she says,” have long sat in honour and in-good-circumstances, but I shall take all that from you, and I lay that [curse] on you, that you disappear (<hverfa>, Z2) away and inhabit a cave and become the greatest troll-woman.
Þú skalt Gríðr nefnast.
You shall call-yourself Gríðr.
Dóttir þín skal fara með þér, ok hverr maðr, sem hana lítr, skal fella til hennar mikla ást.
Your daughter shall journey with you, and each person (man), who beholds her, shall take a great fancy to her.
Þú skalt hvern myrða, er þú sér í hennar sæng.
You shall murder each [one] whom you see in her bed.
Þú hefir átt þér sjau systr.
You have had for yourself <eiga sér e-t>, Z2) seven sisters.
Þær skulu hverja nótt eiga við þik bardaga.
They shall each night, have a battle with you.
Þær skulu alla vega þik sundra, höggva ok meiða, en aldri at heldr skaltu deyja, ok aldri skaltu fyrr frelsast af þessum álögum en þú hittir þann mann, er eigi hræðist þitt it ógurliga sax, þá er þú reiðir þat, en með því at þeim mun þat ógurligt sýnast, mun sá ekki finnast."
They shall on all sides <vegr>, Z4) cut- you -in-pieces, hew and maim, but never any-the-more shall-you die, and never shall-you free-yourself from these curses (spells, tribulations) before (<fyrr…en>) you meet that person (man), who fears not the terrible sharp-single-edged-sword of yours, when you brandish that, but with that [reason] that (ie because) that will appear terrible, that-one (ie he, your saviour) will not be-found (<finnast> passive of <finna>, Z1).