Under copyright law, you may lend the DVD to your friend, but making a copy of the DVD entails circumventing the copy protection, and is therefore illegal.
In any case, if you make a digital copy of the movie, what?s to prevent your friend from passing it on to a few friends of hers? In that case, you become the source of the distribution.
There are a few grey areas in this though. For example, if you own the DVD and it becomes scratched or does not play in certain DVD players, you are entitled to make a backup copy.
Even if you want to transfer the DVD movie to a portable media player like an iPod or a tablet, it is technically conversion of the data on the disc into an unprotected digital format, which can then be shared freely. Bottom line, to be safer, just lend the DVD to your friend once you are done with it.