A big thanks to J_9. Normal, not quite, but often a problem. My feelings is that your neighbors have no business letting their cats relieve themselves in your yard. If they are keeping their own yard clean, perhaps you could take Heidi over there. Maybe put a pile of sand in a corner somewhere and the cats will use it.
Seriously, with it being somebody else's cats, the food additives mean to keep dogs from eating their own won't help. I am afraid you will have to take her out on a leash and try to select clean area. If she does find some, give her a sharp ''Ut. ut, ut!'' and gently pull her away. Six months is a bad age for such. Most dogs eventually out grow it. Not all, my 13 year old Lab will clean up after the deer and rabbits out in the woods if I don't stop her.
As a new dog owner, you should find the material in the sticky helpful. It is mostly meant for younger puppies, it is not too late for you. Start at
http://www.askmehelpdesk.com/dogs/in...tml#post251802
We have some other Mini Doxie people that drop in sometimes. Post any other questions you have.