I think it probable, especially since they encounter RF wasting his money on something utterly frivolous, that this is meant to imply that the were getting money for the jewels.

However, I don't think it's absolutely certain.

Maria Edgeworth also had a scene set in Gray's jewelers in her 1811 novel "The Absentee".

There is this exchange:

'Where are you going now, Sir James?--cannot you come with us?' said
Lord Colambre and the count.

'Impossible,' replied Sir James;--'but, perhaps, you can come with
me--I'm going to Gray's, to give some old family diamonds, either to be
new set or exchanged. Count O'Halloran, I know you are a judge of these
things; pray, come and give me your opinion.'

'Better consult your bride elect!' said the count.

'No; she knows little of the matter--and cares less,' replied Sir James.