In the end it's your baby not hers and it's your choice.

I personally LOVE Ruby and yes it's an old fashioned name but it is very in right now, who cares what she thinks.

And if you do go with Isabella you should sneakily write it in a diary somewhere, backdating it a little and say no see we wrote down our name choices months ago, well before you ever mentioned them... hehehe

My dad came out 100% and said he didn't like Ava before i had her, i said too bad it's a name i like and i'll use it if i want, it's not your baby.
He has never said it again and loves her to death and says it actually suits her... so in the long run even if they don't like the sound of it at the start they will grow to love it and your gorgeous little girl!