MRSA stands for methicillin-resistance staphylococcus aureus which is a bacteria. When you are exposed to bacteria you may become colonized by that bacteria. Once you are colonized you will (most likely) always have that bacteria as part of your body's flora, just at levels that your immune system can control so that you don't present with symptoms and it's not an issue. However, there are times when your immune system can become 'stressed' allowing for the bacterial populations of your body's flora to become unbalanced. When this happens there is a risk of bacterial infection. We see this commonly with auto-immune diseases or AIDS where a person is overcome by bacteria that were once a part of their natural flora or even considered "beneficial" when at healthy levels.
To get at your questions:
This is something she can get future infections from. Is this something you need to worry about? Probably not. Is this something you need to be aware of? Yes.
Will it ever go away? Probably not, she has likely been colonized.
Why is she more susceptible even though she had it in the past? Even though she had it in the past and her body likely has an immune response to control the strain she was initially infected with, bacteria are fast at mutating/evolving and are awesome evaders of the immune system and antibiotics. To put it simply: Bacteria A (with membrane component A) colonizes the body. Bacteria A reproduces creating 1,000,000 daughter cells. Somewhere there was a mutation so that 1% of these daughters have a new membrane component (membrane component B). Now your body was busy fighting off Bacteria A (with membrane component A) and not those with membrane component B. So your body kills off all but the 1% (10,000) with component B. So you still have Bacteria A in your body, just with a different component. This cycle repeats over and over and over. However, this cycle obviously can't happen if you were never colonized in the first place. So that's why your daughter is more likely to get another infection, than some random person getting a first infection.