I don't think you should feel entitled to financial aid from your sister. However, if help from her is your only option then I would go to her and explain the situation. Tell her you desperately need dental work and you don't have the means and maybe ask her for a loan instead of a gift. But honestly I would only do this if it really truly was my only option, because family + money often don't mix well. I wouldn't do it just because of the fact she *could* pay for it if she felt like doing so.