No new car dealers in Penasco. Caborca is closest for new. There is another car rental agency, USave east off Benito Juarez just after the crucero, Do not know if they do long term lease/rentals. Be sure to read the contracts carefully. I have rented from both. Check for liability of repair in case of an accident. Contract terms are different.
There is a small lot with used cars for sale on the west side of Benito Juarez close to the Base Ball stadium. Just a dirt lot with chain link. You have to call him and he will meet you, His cars are all imported but maybe not National and generally fairly nice but more expensive . There are also several areas of the city where you will find used cars for sale parked along the road. Most of the cars for sale along the road are offered by 'dealers'. and not Imported. They are cars brought in from the US, most damaged and repaired for sale here. Mexicali/San Luis is the hotspot for this. Most of the cars for sale have in excess of 100k miles on the speedo and should be checked out with a mechanic. Check the VIN for stolen cars on the internet also !!!
You can buy a US TItled car and import it. There are restrictions on what years of manufacture vehicles can be imported as a National car. You will need a National title to drive in DF. There are agencies at the border who will do that . Costs $1,000 plus last I knew.
You should explore the regulations for who can drive what car and where before you buy. Nationals cannot legally drive a US registered car unless they have the same last name as the name on the US registration and maybe a US Driver License. Non Nationals cannot drive a Mex registered car without the proper immigration status. There are at least two types of imported registrations with different restrictions. There may be more to this than I know.
It is all quite complicated. If your daughter has a US Passport and Driver's License best to buy in the US and keep US registration. She will need the temporary importation sticker which you can now get in Penasco. I believe she can drive that legally anywhere any time.
The real question is why would anyone want to drive a car in DF ???? nuts!!