UK Visa Tier 4 (Early Entry and Biometrics) [closed]

So my girlfriend currently in the US, is starting university in the UK in September on a tier 4 student visa which has not yet been completed as I understand you cant complete until 90 days before.

She plans on coming here (UK) in July on a general visitor visa and staying with me up to the start of uni a few months later.

I understand you have to leave the country and re enter which we planned on doing if we go on holiday in the summer. By which time the Tier 4 visa will hopefully be approved.

Question is will this be an issue, will the UK Immigration get funny about re entry? and would they actually know where you've arrived from? I get the impression its 'technically' not illegal but there could be complications, has anyone done this if so how did it go? Perhaps do a turnaround flight to the US?

Also, is it possible to complete the Visa Biometrics permit from within the UK or as the application is from the US would it have to be done there?

Any advice greatly appreciated!

Thanks