Relax :-)
The airline pressures everyone to sell, it’s very important for ALL low cost airlines. But doesn’t sack anyone who doesn't reach targets. No one has to buy themselves anything. As long as she shows up for her duties (ALWAYS) on time and doesn't "get sick" (this is tricky, cause many just call sick cause they have a hangover - this is not tolerated, my advice, go to the doc and get a cert if she is ever really ill). She will pass her probation easily like that.
She would only be sent home if she would not follow safety procedures or had gross miss conduct (outline on her contract).
Hope it helped.
All the best.