DD2 is invited to a birthday party. No mention of siblings. Can I RSVP and say the following? (it will be via text):

Hi ____! This is _____'s mom _____, RSVP-ing YES for _____'s birthday party! Quick question, can her almost 4 year old sister tag along? I am more than happy to pay for her headcount, or make other arrangements for her that morning. Just let me know!

This is at a bouncy place so I know it is suitable for my not yet 4 year old DD1.

I'm just unsure in case I make her feel bad to either tell me to keep her home, or say she can come but she won't let me pay (but is annoyed that she will have to). I am totally ok with just not saying anything about sibling and having her stay home if need be.