Hi Bub!
I am feeling your pain as I experienced this with DD when she was little. My advice: don't worry about creating bad habits, the mother's group can wait until you feel ready, and trust your instincts and not worry about getting books (save for Elizabeth Pantley's or Pinky McKay's).

Your little Ava is doing what many many bubs do around 4 months of age- a big change in sleep habits. Don't be surprised if her day naps start to become 45 mins each. This is really really common. You have a few choices:
-you can put Ava in the sling for naps so she gets the sleep and is not overtired
-you can try to resettle her each time
-you can try and get her into a sleep and feed pattern

I wouldn't go down the driving to sleep path as Ava will wake up when the car stops. We did this with the DD and the vacuum cleaner! Not pleasant listening to the vacuum cleaner on for an hour at a time, 3 times a day!

Hugh hasn't reached this stage yet but we had issues about 4 weeks ago when he would only be held to sleep. We worked on a routine (with my mums help) for about a week and now he sleeps terrifically. What we did was start a feeding pattern on 3 hourly. I was demand feeding and he was only snacking so he was never full enough for a good sleep. I feed him now (both sides), burp and cuddle, carry him for a couple of minutes, put him down, swaddle his legs (!) and leave the room. He goes to sleep now within a minute. Prior to mum's help he was all over the place as newbies are. I just had to learn the cries and know when he was doing a grizzly one and let him do it. He was not upset and I didn't let him cry it out etc but if he told me he wanted sleep, well I wouldn't go and pick him up. I rocked him lots in the bassinette until the whimpering stopped and then I would stop the rocking. If he started whimpering, I started rocking! This could go on for some time but I persisted and kept it the same each sleep time. I worked on him drifting off to sleep on his own without my intervention. However, I may have been, rocking, carrying, feeding etc mins earlier but those couple of minutes of him actually dropping asleep were done in his bassinnette by himself. If he woke after a few minutes or 15 etc and I knew he was fed, winded and tired, I let him grizzle and lo and behold he fell back asleep. One of my mistakes was I didn't know that he was a noisy sleep and made noises at the end of each sleep cycle, so I picked him up which woke him right out of it. Hope I have been of some help!