A pedantic point maybe, but it's actually your mother's estate which has to pay the money back. If, say, your mother left you a few hundred pounds as a specific bequest, with her will stating that the rest of her estate was to be left to the RSPCA, then it would be the RSPCA (as the residuary beneficiary) who would have to pay the money back.
Likewise, if (after paying off her debts), your mother's estate only amounted to £50, then you're only required to pay that £50 back and not £195. (An estate can't 'go negative', forcing relatives to pay off debts of deceased people from their own pockets).
However, unless either of those two circumstances apply (or something very similar), then I agree that you're required to pay the £195 back.