Is the expression “die alte Huhn” an offense?
A: Kennste Frau X?
B: Die alte Huhn? Ja, die kenne ich.
It should be
If you are saying
"Die alte Huhn" would only work in some regions of Germany if Huhn is the family name of the woman. It wouldn’t be an offense when used by e.g. villagers:
(Old Mrs Huhn told me, that old Mr Schmidt has died.)
"Das alte Huhn" would be the correct translation in your example and is offensive, although I can also image a humorous notion (with B having a long friendship with Mrs X). I would recommend not to use it, you are walking on thin ice.
Animal names like Kuh and Ziege, as proposed by c-p, are more common to insult women, although a little old-fashioned (Sie ist eine blöde Kuh. or So eine dumme Ziege).