Around the gta an off the cuff guess is between $3500-$7000. Depending on how fast you want to sell it, condition and what comes with it. +/-1000 for some unknown fudge factor.
If she's liquidating for a deceased family member than there may be a lot of other related, an unrelated tooling to go with it too. It may increase the price, but alleviate the stress of her having to piece it all out, and stretch it all out over a few months to years. Having someone come in to buy it all, might be of great value to her, and opportunity exists for both parties to be very happy with the deal.
Looks like a nice lathe. The first metal lathe I ever used was a similar brand new colchester they'd just got in the Durham College machine shop. I've always like those speed selector dials. But I've always disliked the backward carriage/cross slide feed handles of British iron. It just feels unnatural to me and makes me uncoordinated.