You keep saying that your sister won't have a problem with giving you back the money, but that you also want a solicitor.I don't believe I will have a problem with my sister giving it back but want to know exactly where I stand before asking for the shares or whatever to be returned as I am a little cynical when it comes to these things. I want to approach her with a viable plan in place.
My sister left me with the impression that returning the money would not be easy. I shall look for another solicitor
Which is it?
To my mind, if you are still resident in the US you need to establish what your position with the IRS is and whether your debt there has been dealt with.
Once that is established you will know whether they will come after you if you have more money.
Other than that, you don't need a solicitor to ask your sister to give you money. That's just a conversation between you and her. You have no legal title to the money, so you are reliant on your sister thinking it's a good idea to give you the cash back.