The trolley will be crowded. If you don't mind the crowd and the travel time, it's a cheaper option. It's $2.50 one-way per person over 5. So if you're daughter is older, you're looking at $10.00 per day round trip. You can always Lyft or Uber it in. For me I don't mind taking the trolley but that is only if I am by myself or riding with other adults or older kids. If your daughter is little, you might not want to be on a crowded trolley. I wouldn't. There is a lot of walking at the con. So walking to the trolley, plus the crowd on the trolley and at the con...might be overwhelming.
That said, If I had the money to comfortably drive in and park close to the con, I'd opt for that. Lol. As far as Mission Hills, I don't know the area. But you can check it out via Google Earth. That's what I do, so I can get an idea of what the area looks like.
Good luck! And have fun. SDCC is a lot of fun, especially the first time. 
It never makes sense to buy a one way ticket on San Diego public transit unless you are only going one way. The price of a daypass is the same price as a roundtrip. If you buy a multiday pass then it's cheaper.
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That's the place I was talking about in the hotel thread with very nice rooms for $129-$149 even during comic-con. They aren't raising prices. But it seems they are too far away and no one cares. There has been at least one comic-con offsite held there in the past. No need to take their bus to the trolley to get to comic-con though. They have shuttle buses that run directly to downtown San Diego including one that drops you off right at the convention center. So you don't even need to pay for a trolley ticket.
By the way, their downtown San Diego property is the US Grant.
The trolley shouldn’t be too bad until you actually get to old town. I’d personally skip driving.
Going to comic-con during the day the trolley really isn't too crowded. The crowding happens at night when everyone is leaving at the same time. I take the extra 5 minute walk to the end of the line and hop on there. Very few people do so there are always plenty of seats. The next stop at the convention center is where everyone gets on.
Not just multi-day discounts, but they will also offer a special SDCC pass for all 4 days.
In the past, the special comic-con pass cost more than the regular multi-day pass if you already have a compass card. It's wasn't much more expensive, like a dollar. It's one thing if you want the physical pass as a keepsake. It's another if you are just using the compass app on your phone.
