Yes, looks like a laudable campaign, but using misogynist words and imagery is unacceptable and undermines the message completely.
The first paragraph of your reply looks good. For the second, perhaps something like this . . .
We support your aim of highlighting the irreparable damage caused by decisions of Newport City Council planning department and Sheila Davies role in this as Head of Planning. However, using a sexually degrading, sexist statement against her because of her gender identity is unacceptable.
It would likewise be unacceptable to use racist statements to criticise the decision of a Black council official or homophobic statements against a Lesbian or gay official.
Also, use of sexist material draws attention away from the purpose of the campaign and is likely to alienate many who would otherwise support it.
I think I would drop the last paragraph though. After all, I've seen sexist content generated by women (perhaps internalised sexism or just lack of awareness,) and last thing you want is for them to come back and say, "Well yes actually, the idea came from a woman in our campaign," because that would just derail the point you want to make!
I'd suggest raising that they wouldn't think of doing something similar about a Black, Gay, Disabled, etc., Council Officer will be more likely to get a re-think.
Good luck whatever you do,