(*Kindly do not post on website*)
Assalamualikum,

A relative of mine wished to purchase a pair of shoes from an online store. She chose the shoe, saw the cost price (not including

shipping and duties) and gave me the link to buy it for her. She said at that time she would pay the costs for it.
Before buying and paying for this pair, I also saw another pair of shoes on this website for my mother and told this relative I would buy the shoes for her and pay for it and she did not object to this. I therefore purchased two pair of shoes from this site and combined the shipping costs and when it arrived here, I paid for the duties collectively (note the duties were calculated differently for each, but the receipt I have only shows one figure as the Post Office does not itemise).
When the items came, I told this relative about it, and she came to my house, having been given the shoes for her by my mother.

She had them on before I could come out to greet her, and I told her to take them off as they are not hers as yet. She did this, and I then handed them over to her, saying 'here this is a gift for you', to which she accepted, said 'Thank You' and took them home.
Now, about two weeks later, she decides to pay for them. She said she wanted to pay for the item, and I told her I would not accept any payment. She then sent by me a sum of money in US dollars far in excess of what I paid for her item.
My question then is whether or not I can accept this money, as I am concerned of the following:
(1). That the gift having been accepted by her now rests in her possession, and thus how can I receive money for an item not owned by me?
(2) Alternatively, she would have undertaken to pay the cost I incurred in acquiring the item- which is a fixed amount (different from value of the item). As I said I intended to pay for the item for her and thus grouped it together with something for my mother. Thus, it is almost impossible to calculate the exact cost (re duties and shipping) I incurred for this item, and my concern here is then whether accepting more or less of this fixed cost would be counted as interest? For example if it cost me $77 and I took $75, or even average it to $80 would this be ok?
Finally, as I said she gave the money in US dollars, and the currency rate at that time is different from now, and the money charged from my account was charged under my local currency. Is it then permissable to accept this US money? Would I have to pay back in local or US?
In this situation what should I do- return the money? keep all the money she sent? insists for a return of the gift (as she expresses to pay for it so she thus rejects it)?
I would be grateful for your islamic advice on this matter.
JazakALLAH for your time.
-Abdullah