Translation:She has to complain.
My mnemonic for gwyno is that it kinda sounds like whine
Is the un-mutated word for "complain" "cwyno"?
Yes. cwyno - complaining, to complain.
If you use www.gweiadur.com (registration is free, and the dictionary is very good), or Ap Geiriaduron on a smart-phone, it is very easy to look up the mutated and unmutated forms.