Could I have handled this better?

Why would you expect your mom to write you another check?  If you're that careless,  you would probably "accidentally' throw that one away too. 

Your question doesn't make it clear whether you ever SAW the cheque at all. Did you see it, and then it got lost? or did you never see it at all, and are relying on your mother's word that she did in fact place the cheque in your purse?

I think your answer to this might help us solve the problem.

She sounds like she feels you are careless with money.  If you can afford the trip, does it really matter?

If your purse is anything like mine, I might never find a small piece of paper that someone else put in there.  Between the store receipts, the crossword puzzle pages, the day's mail, and so on, chances are it would never be noticed.

Recently my husband came to me and showed me a check from his father (now deceased) which would have gone a long way to propping up our budget at the time.  Oh, well ...

Perhaps your mom felt that you no longer needed that money, since your trip was already over.  I imagine she'll be generous when the next gift-giving occasion rolls around, and wiser about it too.

No it is not odd, she likely changed her mind.

is it possible she re-thought the check and removed it herself?  maybe she really couldn't afford it and did a last minute grab for it...but thought you might have seen it and mentioned it.

or maybe you were talking about something and she got ticked and removed it?  I just have this funny feeling she took it....or why wouldn't she offer to write a new one?

maybe shes afraid you'll lose it by accident again

You could have handled it better.  You could have thanked her when you found it rather than waiting for her to call you.  You could have admitted to finding it before and being careless rather than allowing her to believe she was partly at fault.  

Because she didn't owe the money to you, she is under no obligation to replace what was lost.  And it sounds like you were apologetic for losing the check, but didn't offer appreciation for the gift in the first place, thanking her for it or her effort to surprise you.

T wasn't smart that she secretly put a check in your purse. Maybe we'll intentioned but not a good idea.

Yes it is quite odd that she has not offered another check in my opinion.