Correct on both accounts if your lo is taking 45 min naps. Usually that's a telltale sign of it.
At around 4 months seems to be the heart of the daysleep organization. What you do is extend awake time by 10-15 mins over the course of a few weeks until she's up to 2 hours.
And yeah, mornings you have shorter waking periods. Part of the reason for this is because the morning nap is (in theory according to research) an extension of night time sleep, because you get the same sleep pattern (length wise of each cycle) in the nap as your early morning sleep period (between 4 and 6). So...if you're putting your lo down at 1:45, you can probably put her down at maybe between 1:30 and 1:35, perhaps even a little earlier, and get a good 1.5-2 hour nap.
However, because day sleep is developing, I wouldn't bank on getting long naps for awhile on a consistant basis no matter what you do unless your lo pretty much sails right through it (you'd be the envy of a lot of moms!). It usually takes 3 weeks or so to sort itself out.
Hope this helps!
*HUGS*
Sonya =P