Nurse pressed down on glabella area AFTER Botox injections, made me feel uncomfortable for a long time and wouldn't let me up.

Pressing down on the area to avoid a bruise is ok. Massaging the area or adding excessive pressure after injection should be avoided for 24 hours.

You probably had some bleeding at the injection site which the nurse was trying to control with pressure. This is not unusual. You just don't want to massage the injection site for risk of spreading the Botox outside the intended treatment area.

Very difficult to disperse the material with pressure into the orbit so nothing much to fear by pressing down on the glabella to prevent obvious bruising.

You should not massage a Botox area.  Pressing down on a site to suppress risk of bruising is fine.   Of course logical and not excessive pressure is needed.   I generally do not press unless I see a little bleeding from a given needle stick.  My Best,  Dr C

Most likely she was trying to avoid a bruise.   Most likely you had a bit of bleeding/oozing and she was trying to control it.  I wouldn't worry too much about it.  

The only time we press - moderately, not hard - is when a bruise is apparent or blood comes out right after injection. This is to ward off as much of the bruise as is possible. It's not dangerous, when you know what you are doing and doing it correctly. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."