Buyers solicitors trying to re-write deeds (leasehold) looking at £1000s

I’m just in absolute bits. We bought a flat a few years back and it has done us well but we have a toddler and another baby on the way so needed to upsize to a house! We found the house of our dreams, which was no chain and were over the moon when our offer was accepted below asking price!

We sold our flat to a lady with a short-ish chain (4 altogether). We’ve been waiting for a months and months now to get things sorted as our house has been ready for a while now, and finally get told today by our solicitors that the buyers solicitors does not like the lease. They have raised around 50-60 enquiries about the property and the lease. They don’t like some of wording of it, and say they want it re written (deed of variation), which could cost up to 1k or more. They have also raised issues with the head lease, and our solicitor has said that this is a very complex change to make as would involve the landlord and other leases etc… and would be very costly. I believe the buyer is purchasing without a mortgage also.

I am just absolutely baffled. It feels like her solicitors are trying to make as much money as possible out of a cheap sale. We aren’t able to contact the buyer directly. I just want to move at this point. We are trying to communicate through our estate agents on what to do. We just hope she ignores the solicitors advice and proceeds anyway. We’re all living out of boxes at this point. I just don’t know what to do