I think it is difficult to acquire the skills which aid tyre-changing in that it only happens irregularly. For people with small hands/weak hands, there can be no better tool than the "VAR" tyre levers. This because they use the "lever" principle to haul over the remaining section of tyre rather than struggle to push this with the thumbs. In the link you will see that one lever is designed to fit on the opposite side of the rim from the section of tyre needing pulled up. The idea is that you hook the curved part of the lever over the last remaining section, position the slotted portion of the lever onto the opposite rim, and pull up and over. I've used them for over twenty years and never have they failed.
http://www.cyclebasket.com/products....d=m5b93s281p92