Basically yes
To reduce the risk of Osteopenia you need adequate amounts of calcium, magnesium, vitamins D, K, and C as well as other minerals.

In order to absorb optimum amounts of calcium your vitamin D level MUST be above 80nmol/l = 32ng/ml (but ideally higher than that to reduce risk of other conditions)
When your 25(OH)D is above 32 you should be able (providing you eat plenty of good food sources of calcium) be able to solve the calcium shortage without resorting to supplements BUT it's likely you'll be unable to get sufficient MAGNESIUM from your diet so supplementing with magnesium as well as vitamin D is worthwhile.

So low vitamin D caused low intake of both calcium and magnesium BUT while raising vitamin D to above 32ng should correct the lack of calcium without extra supplements it's possible you could still be short of magnesium.
Vitamin K2 foodsources also need checking.