working for EU company (remotely) with Swiss residence

Background:
My wife and I are EU citizens. I have a job offer from a Swiss company, so we are relocating soon. Then I will apply for my permit B. As far as I understand, my wife can apply for a permit B too (once I have mine).
However, my wife currently works on a permanent contract for a company in Poland, so in this situation, she will have to resign from her full-time permanent contract. The company is not willing to have an employee with a Swiss residence on a “permanent contract” (but we know that it might be possible to continue working with another form of cooperation)

We would like to understand how she can act proactively and what she can propose to the company. What are the possible options - before her upcoming conversations. She wants to act proactively to keep her job. She likes working for them and wants to continue her job.

She is not seeking employment for a Swiss company at the moment (at least in the next 10-12 months). She just wants to continue her work with the company.

We have started exploring the topic recently and found these options:

Sole proprietorship registered in Switzerland
My wife will need a permit B (but as understand she will be eligible)
Disadvantage:
The main problem is that she will have only one client for now and as far as we know, sole proprietorship requires having more than one client (at least 3 clients). Otherwise, the Swiss authorities could consider her as an employee, and we want to avoid anything illegal.

Umbrella company / payroll company
As far as I understand, in this arrangement, a person becomes an employee of an umbrella company on a temporary contract, so there is no need for 3 clients. Also, there are no administrative problems related to sole proprietorship (self-employment).

I found some companies such as: PayrollPlus https://payrollplus.ch/en/ Helvetic Payroll https://www.helvetic-payroll.ch/en/ Accruity https://www.accurity.ch/ Diligo https://diligo.ch/ Thalent SA https://www.thalent.com/

Could this be a good solution?

Alternatively, if this does not work out, she would like to understand what are her options for working remotely for other similar companies in the EU/Poland but working from Switzerland (for the next few months).

Most importantly, we want everything to be legal. I do not want my wife live on a “tourist visa” and work remotely. As we understand, some “digital nomads” might probably work illegally while being on tourist visas. But we does not want to do anything illegal.

Does anyone have experience or a similar case and can share their solution?

We want to understand, at this point, what are the available paths (once we have some background on possible options, we will most likely speak with a tax consultant).

Any information would be highly appreciated. Thank you.

Check also out ANOBAG (and search on the forum). There have been several threads on tihis.