:salam2:
If you're looking for books about the Prophet
then please buy from Muslim scholars, however if you're looking to buy books on Islamic history then I would say go ahead and buy her book. She is probably one of the most respected (by Muslims and non Muslims) of the oreiantalist.
The Imam at my masjid said her book on Prophet Muhammad
is not bad at all.
The reason I'm saying this is because there aren't alot of literature about Islamic history by Muslim authors that have been translated. I'm not sure if you know arabic, if you do then I suggest you buy books by Muslim authors.