Excellent advice given , I Will add my two centavos.
Any of the Texas border crossings into Mexico will work fine.
Just this year I have used Reynosa,Aleman,Piedras Negras and
Juarez and encountered no problems of narco violence nor
did I see corpses piled roadside .
I would even go so far asto suggest that in order to a very early
start on your ride away from the border that you actually cross the
Rio Grande in mid to late afternoon at either Matamoros ,Reynosa or
Nvo Laredo and get the paperwork done at their clearly identified
border Aduana facilities , then with lots of daylight left pick one
of the many good hotels in the city enter area on your route and get
a room for the night. Really,they are very good ,cost less than on
the US side and are quite safe even for you as a woman traveling alone.
These city centers are not the shooting
galleries US media stories make them out to be.
If you chose to
cross at Piedras Negras you would not even have to worry about the
customs process since that is done at Allende 53km to the south.
Also before dark ride around a bit ,visit a Mexican restaurant,even McDonalds ,BK or whatever familiar US chain you see .Then back to the hotel
and securely park the bike, see theTV News for any thing which would
impact your ride and get a good longnight of rest.
Next morning you will be fresh to tackle the ride out of town
and notbe worried about running out of daylight before you.
feel far enough away from the perceived dangers of the border.
Send me a pm if you would like some directions to a good hotel in
the MEXICAN border town you select
And Mex 180 is not as boring as Mike makes it sound. wave:

You just need to appreciate the colours of the paint,it's texture and
variety of application techniques

I.e. the subtle variety in the natural landscape