|Relax, you can be a good mother to a single chihuahua and still work full time.
I am going to assume you are getting a new puppy, if I am mistaken some of this will still make good sense, some things you an ignore.
What I did is make sure that I had at least a three day weekend off. Bring the puppy home the morning of the first day off, not the evening before. The puppy will be much more comfortable at nighttime if it has had all day to get used to you and its new home.
Ask the breeder to make sure there is something which you can take home with the puppy that will have the scent of its mother, or its old environment. This will help comfort the puppy and help the transition to being comforted by your smell.
Plan to spend a lot of time with the puppy, pet it, let it sleep on your lap, spoil it rotten, it won't hurt for a day or two, it's as impossible to spoil a brand new puppy as it is to spoil a baby human.
Decide how you want to deal with potty, I used a litter tray since MN is not chihuahua friendly in the winter. Also, since I was going to be away during the day, she wouldn't be trying to hard to hold it if I got home later than I expected. If you decide she should go outside, then start from the very first. There are other threads here related to how to train a chihuahua. Also decide where she will have her food and water.
From the first, your puppy should sleep in her own bed. Some people use a crate with a warm fabric bottom and something for puppy to curl up under. I used a cardboard box for my girl with a towel in the bottom and a blankie to curl under. The first two nights, I put her in my bedroom next to my bed. She cried at first, but just like human infants, you have to tough it out while they learn to sleep on their own. This is where that smelly object from their previous home is used. During these two nights, you will create an object with your scent on it, I slept in an old t-shirt.
I planned to use my bathroom as her place to stay while I was away at work and where she would sleep, so I would put her bedbox in the bathroom and put her in there too for brief periods of time during those two days. Again, she would cry, but if I made sure she was good and sleepy first, it didn't take her long to fall asleep.
The third night, I moved her bedbox into the bathroom, which had a tile floor. I left food and water for her and also her litter tray. If you use a crate, do not put food and water in with her. Dogs don't like to soil where they sleep, but if a puppy eats or drinks it will have to 'go'. Once a dog gets used to soiling its bed, it is almost impossible to break them of it. This is where the item you will create with your scent on it is used.
When I went back to work, puppy was greeted, encouraged to go potty, cuddled, placed back into the bathroom and I left. Make the departure low-key, tell her "Mommy is going to work now, but she will be back later and she will play with 'insert her name here'." When I got home, again arrival was low-key. I entered the bathroom, encouraged her to go potty, and then spent the evening with her again on my lap snuggling and being petted.
A chihuahua will bond to one or two people, you will become the center of her universe, so it's not strictly necessary for her to have a playmate, at least not at first. I did get a second chi a year after the first, it was much easier since her older sister trained her where to potty, etc.
A chi will need attention from you, if you don't want a dog who wants to be with you all the time, a chihuahua is not the dog for you. I suggest getting the book Chihuahuas for Dummies. It has lots of useful information about the care and training of these adorable furry creatures, and is the best book I have seen, so I recommend it a lot.