This is purely anecdotal, but both of my children used a baby walker (the mobile frame with sitting/standing support) for a couple of months, at around your DDs age. I've got to say that it wasn't something we planned for, but the walker turned out to be an excellent solution for our active, motivated-to-be independent children (and for me to have my hands free for a few minutes again!). I'm aware that walkers are somewhat contentious in some circles for much the same reasons your MIL states, but in our experience its use did nothing more than provide DS and DD with a safe way to explore autonomously, during that in between stage. It was a short-lived period anyway with DS walking alone by 8 mos and DD by 9mos, as may be the case with your DD. I personally believe that absolutely nothing could have hindered my children's attempts to get up and go (aside from the unthinkable... forcible restraint), and suspect your DD will continue to do just as she is doing, with or without your MILs approval
All the best with your little one
