Deposit trouble-What to do?

So I'm in sort of a dilemma and don't know what to do. A woman contacted me when Taffy's pups were about a week old, and was interested in purchasing Zero. She just moved out from her parents not too long ago. Her parents had an isabella dachshund that they wouldnt let her take with her so she was happy to find someone near her that had some. She was real nice and genuine when I talked to her on the phone, and through her emails. She had told me she sent out the deposit late Wednesday (March 23) from Buffalo, NY. Now my dilemma is we still have not received it....considering it has been almost 2 weeks since she had stated she sent it out I am having my doubts that she even sent it. I had another family call me last week that was interested in Zero, and I told them that he was pending and I would call them and let them know if the deposit falls through. I'm really unsure of what to do because I don't want to sell Zero to another family if she isn't lying and the money order got lost in the mail, but I don't want to wait forever for a deposit that is never going to come and waste my time and the other family's time waiting.

This is what I emailed her this past Saturday:

We still did not receive your deposit. You had stated you mailed it out last Wednesday, if you did not mail it because you are unsure about purchasing Zero please let me know as I have another family that is interested in him, and has been waiting for me to confirm whether or not he is available. If you did mail it out you may want to check with the post office you sent it from. We normally do not hold pups while waiting for deposits longer than a week, and it has been about 3 since you first contacted me. If you really did send it we are willing to work with you, but we must get this thing figured out.

This is her response:
I'm in Atlanta on my vacation/birthday trip until Mon. I have no idea what could have happened! That's so weird, I'll call my parents to see if it was sent back. If not, I'm going to get in contact with the post office. I'm really upset now. I don't understand what could have happened. I do have the receipt for the money order saved as well

Any thoughts?