If a Muslim woman can limit her work at the beauty salon to doing only what is permissible, then there is nothing wrong with that. Otherwise, she should look for another job.

It is haram to make money via the White Sands app since it is based on gambling because of the stipulation to pay money in advance, whether monthly or annually.

It is permissible to work as an intermediary between service providers and customers. This comes under the heading of brokerage. That is on condition that the service agreed upon is permissible. For more details, please see the long answer.