Trying to figure out best care for my Mom with Alzheimer's...get outside help at home, assisted living, move in with her. How fast is decline?

Mom is 81, lives alone, recently diagnosed with mild to moderate dementia. Doesnt want help, but cant take care of herself. Looking into day care and facilities here, comparing that to in home care. Debating whether to take the time now to spend more time with her before she declines further, while she's pleasant to be around, but would need her to in effect pay me, as I cant afford to not work. Also taking care of my own home and teenager. Feeling stretched thin. Any advice?