Is there a way to do this on Subeta? I can't figure out how.

ask your friend to create a Trade and tell you the lot number, Search for it by that lot number and offer sP on it.

OR

Do it the hard way and go to the sP Voucher Exchange which you have to Google as it is not on the map, and exchange your sP for vouchers and sent those physically to her.

Ask your friend to set up a junk trade and offer on it

Thank you very much. I can't believe I forgot we could do that.

you are welcome. I wouldn't have done very well when I was new at Subeta if friends hadn't helped me.