If you ask your sb to spend christmas/new year/birthday with you and she decline. what is your reaction to this? i mean i know this isnt a real relationship and she has no obligation to spend those days with me, but in the back of my mind, i feel like if she is not appreciative enough to spend a least one of those days with me, then its a deal breaker for me?
I'd say it depends.
Christmas and New Years depending on her nationality are very important days for Friendships and Family. So asking her to ignore familial obligation for you, even if you had a traditional relationship of Boyfriend and Girlfriend might even be asking a lot.
Certainly one way or another you have a relationship, but I don't know the details of that relationship to really make any judgement if your request here is fair or not, after all if your relationship is one where you are polyamourus, she is a married SB, you are a married SD, you and/or she have other relationships, or a lot of big obligations elsewhere, then while I would hope she would spend a substitute type day with you, (i.e not Christmas day but a Christmas party sometime in December for just the two of you) it's a little demanding of you to expect her to spend these big holidays with you, or to expect her to invite you to parties or events where maybe you won't know anyone and there would be an uncomfortable explanation of who you are and why you are there.
Your birthday however I would hope she would try to celebrate that with you if you invited her! I mean life happens and she may have another engagement that day if you don't ask far enough in advance but it is your special day so she should try at least a little to do something special with you.
Her birthday it depends on her feelings towards it (and if you know when it is.) Maybe she doesn't celebrate (I haven't since I was 14) maybe she likes to have a big event with her friends, maybe she just doesn't plan anything for it and that would be up to you to ask and do something for her.
Honestly all of these depend on the exact nature of your relationship, my roommate does special events with her SD but that's the nature of their relationship, if these all feel like dealbreakers for you then tell HER that, the whole point of a sugar relationship IMO is to have a relationship where you can actually be genuinely honest with your partner about what you want and expect. If she doesn't agree then you can offer more money to get her interested or cut her loose and find a SB who will connect with you in the way that you want.