Well, I have been looking through the books for LHFHG for the past week and my dd has been VERY curious about them!
I kept telling her that they are her new school books. She kept asking when we would start and finally on Saturday morning (her daddy was at work for the morning) I decided we would go ahead and dig in. We ended up doing everything for the first day except storytime. She loved all of it, especially the rhymes in motion and the CD song to go along with the Bible memory verse. So all in all it went well. The only hang up I have is this... We did the history first while and it did seem a little bit over her head. Toward the end she said, "this is a long one!" She did well with the devotional. It asked engaging questions throughout, but again it seemed to kind of go over her head. She is definitely ready for begining handwriting instruction, beginning math, and we have been doing phonics for the past 6 months with great success. The only thing is that the "right" side of LHFHG seems a bit over her head at times (although she does love the rhyme and the music part). SO, here is my thought for right now. I still have the LHTH guide from when I did a bit of it before when my dd had just turned 3. She only did parts of about the first 10 units. Should I just go back to LHTH and start at Unit 11, but add in the handwriting, phonics, and then math (using the LHFHG guide for the hands on to go with Singapore)? I was planning to do about 2-3 units a week of LHFHG until the fall and then maybe pick up speed, but perhaps doing LHTH at full speed would be perfect. We will take some brakes through the summer, but will pretty much keep right on going. I figure we can do alternating days with math and handwriting and do phonics 3-4 times a week. If we start at Unit 11 in LHTH then we would finish sometime in the fall and then we could go straight into LHFHG at full speed. Does this sound like a good plan?
So, all that to say, take it slow and enjoy your time with your daughter.
) but I'm thinking that it would be nice if you weren't always off the daily HOD plans for the math like you will be if you start the LHFHG math plans along with LHTH. The phonics and handwriting wouldn't be that way - they're both kind of a "just do the next thing" deal - and maybe the being off in math wouldn't bug you (could just be me 
). But also, I'm just thinking if you look at the placement chart and think she fits best in LHFHG that you may find yourself adding and adding to LHTH because it's a bit young for her - in which case, it would just be easier to do LHFHG half-speed and let her grow into it. However, this is totally your call - you will know best for your dd! 
I just wanted to encourage you that my 4.5 yo that started LHFHG half-speed needed about a month to settle into it - and then it was a perfect fit. Probably either option would work fine.