Concerns about teenager's vision?

My teenaged daughter has been squinting a lot over the past few months. I finally took her to an eye exam yesterday and it turns out that she is suffering from a vision condition called myopia that requires her to use glasses. Unfortunately, the doctor didn't go into much detail about the severity of her condition or the need to wear glasses constantly. However, he did say that she should come back for an exam in 6 months because it is very likely that she will require stronger glasses once her eyes adjust to the current prescription and begin to relax. The prescription is as follows:

OS -2.00
OD -2.00

The edges of the glasses do have some thickness to them but that might be because we opted for the cheap lenses. According to my daughter, her friend Sally has been wearing glasses for 3 years even though her vision is currently only -1.75. This worries me quite a bit. Is it likely that her eyesight will get even worse in 6 months time?

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