student visa after getting the visitor visa

[samiraz]

My friend has recently received her visitor visa for the uk. She has been enrolled to a MSc in uk which starts on 29 sept. She wants to come to uk for 4 weeks in the month of July. Can she apply for her student visa before she comes to uk for visiting ? will the embassy show any issues with her having an unused visitor visa and her applying for student visa ?
if she applies after going back from uk, will the embassy show concern that she has stayed there for 4 weeks ?
Which option is better, to apply for student visa before she comes or to apply for student visa after she goes back?

Thank you for the advice