Its an absolute hard no to taking her from me!
She doesnt have to like it to accept it!
What you are looking for here is her happy agreement- you're not getting that so you're considering backing down. DONT!
The event doesn't become any more age appropriate just because she's sulking!!
Our job as parents is not to make our kids happy every single minute! We also show our love and care by setting clear appropriate and consistent boundaries. supporting them with their disappointments and modelling how is appropriate to behave when things dont go our way. Not by wanting to be their best mate.
I always used to say to my kids "you may not like all of my decisions but please know I am making them with your best interests at heart" and "if you choose to make yourself miserable about it, that's your luck out!"
If she says she will refuse to speak to you (she will soon get bored of not talking to you!) Id just say something flippant and sarcastic like "you do you dear" and "oooh peace and quiet!" Hahahah
Equally id also try to have a compassionate conversation where you acknowledge her disappointment , whilst maintaining the boundary, and sharing your rationale for WHY it is age-inappropriate (in simple terms) and when it would be appropriate in future. And also letting go of your need for her to be happy about it.
As for the pets, if she refuses to look after them then thats a simple consequence, they get rehomed to family that is willing to look after them, because they are her pets not yours and Dh's, and you have enough grown up responsibility already.
She'll probably sulk a little while longer yes, but that's way better in the long term than her ruling the roost and accessing inappropriate stuff too early.
Out of interest, you say DH did everything for her but has now stopped. Why did you, as her other parent in the same household allow this? And what has changed now?
It seems a little bit of a controlling dynamic, where everyone is subservient and scared of a child, who has become spoilt and entitled!⁸