Taxes when employed and earning residual incomes

Hi, I'm completely new to this forum so my apologies if I make any newbie mistakes.

My wife and I moved to Spain last year. She has not been working, to date, but is preparing to send some of her art to France for an exhibition in February. The gallery owner is insistent about paying her for any sales without VAT using the intra-community system. This part is fine, as that's the way I bill my clients and we've arranged for my Gestoria to accompany her to the Hacienda and Soc Sec office next week to register as Autonomo. Due to the uncertain nature of the art buying world and the need to pay the Soc Sec fees, we've also established a full online art marketing business plan that, when implemented, would also provide a continual, albeit probably quite low, income stream.

As fate loves to play games, today she has also been invited for a job interview for a position that she is quite keen on. If she was accepted for the job, what would be the best way to handle the potential income from the art? What happens regarding Soc Sec payments? Would she be covered by the full time job or would it be better to persuade the employer to take her on as an Autonomo?

Any advice on this would be much appreciated.

I've got so many other questions to ask as well, but they can wait for another day.

Saludos