Who said anything about her selling the house? The situation is existing. The A/C is existing (10 years old according to the OP). There are no existing problems (according to the OP).
The only thing new it seems is the boyfriend.
Come on Petey, you know some HI is going to say the panel looks overloaded and needs to be upgraded. Then there is the HO that thinks they need it and want a price reduction even when shown the facts that 100 amps is adequate.
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.