Take a leaf and check under the magnifying glass. If you see a lot of tiny little mites crawling about, then that's a clear problem. For a single rose, the best method is manually treat it. You can pinch off heavily damaged leaves. The rest you can rub your fingers to squash the bugs. Then give it a spray of real insecticide tothe undeside of the leaves (put teh pot on a high chair or table). In this way you don't have to spray it more than 2 times.

Another alternative is to use strong water jets to spray the mites off the leaves. You have to do it 1 time each day for over 1 week.

Also move the plant to a cooler and breezy place. This will help (morning Sun and sheltered from afternoon Sun would). The mites like it hot and dry.

Regarding pruning, you cannot do it to young roses especially when it is not healthy. You just have to wait until a young rose become strong enough before pruning. Feeding young roses can be tricky too. You may feed it at the wrong time. You may burn the roots. I find that the best policy is to bury/put the pots of young roses on fertile soil. The roots will eventually get out of the pots and look for a feed all by themselves. This is slow but surer and almost always produce the best results.

With own root roses you have to be very patient. I fyou graft roses on a root-stock, the result is much more consistent and faster.