I don't know anything about whether VA Tech tends to fill up their scholarship spots. That may be a good question for the NROTC staff there. My DS is a 4/C at U Mich and loves it there. When we visited, we were told they rarely, if ever, fill their scholarship spots, because the university is so hard to get into. U Mich has an acceptance rate of about 28%. A quick search showed VA Tech with an admissions rate of about 71%, so my guess would be that it may be more likely to fill up. Looks like Georgia Tech also has an admission rate of about 25%, so my guess would be it's less likely to fill up. Keep in mind though the information above about the reduction in 4 year scholarships, but leaving the same number of scholarship spots at the units, so units are less likely to fill up. If your DD is confident she likes VA Tech better than GA Tech, it might be a good idea to move the scholarship to VA Tech now. She should be able to move it again, as long as there is space where she wants to move it. My suggestion would be to talk to her about what type of setting she sees herself in for college. GA Tech is in Atlanta, a major city; VA Tech is in a smaller city. Purdue is also in a similar size city to VA Tech. U Mich is in Ann Arbor, a city of around 120,000. Each will have their own feel and personality. It's great that you are able to visit all of them; there's nothing like being there in person. My DS and I visited U Mich, Purdue and UIUC spring break his junior year. They were all great schools and each definitely had it's own feel. UIUC was on spring break when we visited, so it was hard to get a good feel for the school without students there. I hope school will be in session when you visit.
If I can give a little advice, based on my experience last year; listen to what your DD wants to do about the scholarship. You can give input, but it's ultimately her decision. She has obviously made good decisions to this point, because she has so many great options to choose from. I know this is nerve wracking as a parent right now, wanting to help your child make the "right" decision. I think they handle it better than us sometimes; my DS was definitely calmer about his decision than me last year. His scholarship was placed at U Mich in November. In December he was deferred during early action. I suggested he may want to move the scholarship to Purdue to hold a spot there since it was his #2 school and he was already admitted there. I suggested this knowing U Mich told us they do not fill up, so he could move it back if he was admitted. Ultimately he told me he had a good feeling he would be admitted to U Mich and didn't want to move the scholarship. He was in communication with the Admissions office and NROTC adviser. He was admitted in February. The waiting period about killed me, but he seemed calm and confident with his decision.