Hi Laughalot:
First off remember that in many countries children do not formally start school until the year they turn 7 and they end up doing as well or better than British children. So start off by remembering this is a marathon not a race.
Sounding out/ blending help: try getting in some jolly phonics workbooks - but then really reinforce those sounds your DD is working with in your reading. (i.e. if she's learning sh- sounds - then make a point of having her sound out all sh words (maybe with a bit of help from you) in whatever you're reading.
Reading: Make sure this is a regular feature of your day. We do this after bath and before bed time. You may be doing the bulk of the reading right now - but you can include your DD by identifying words she should know (high frequency words: www.saintambrosebarlow.wigan.sch.uk/Infant_spellings/infantspelling.htm & select H/F words list 1 and 2). Start regularly pointing to them and have your DD read those. Gradually you'll move from your DC reading one or two words per sentence to reading whole words.
If you haven't come across it - OXFORD OWL has a lot of advice and useful on-line e-books for free: www.oxfordowl.co.uk/Reading/
MATHS: This is really up to you and what you're comfortable with. It may be that you have strong skills and can support this yourself. Oxford owl also has a maths section for early years, which may help. One thing I picked up on with my own DD1 (who also was very behind in KS1) is that she learned maths better through visual examples. So lots of raisins, smarties, buttons, etc.... and drawings to support explanation in workbooks. Ultimately we opted for an on-line tutorial which focuses on basic calculation skills (mathsfactor: www.themathsfactor.com/) but others here on Mumsnet have sung the praises of mathletics (www.mathletics.co.uk/) and mathswhizz (www.whizz.com/)
For Year 1 - the real aim is addition/ subtraction with numbers up to 20 and counting by 2, 5 and 10 (early multiplication tables). The real hurdle for us was numbers over 10 - but this can be shown visually by working from the start with units and tens and making sure your DD can visualise the difference between them: so for example in the number 24 the 2 = 2 tens and the 4 = 4 units. The best way of explaning this is using two different but related items. We used grapes (for tens because they were nice and big) and raisins for units. So 24 = 2 grapes and 4 units. To then take away 10 from 24 would be the equivalent of taking 1 grape away. You can also teach borrowing by cashing in a grape for 10 raisins.
Games like snakes and ladders can also really help with counting on (playing forward) and counting back (playing backward from 100 to 0). To increase numbers you're counting - use two dice.
I've been there - but if you take a deep breath, accept this is going to be a long, slow haul and just keep plugging away at it when you can (30 minutes or so a day max including reading time and ideally not in one solid go) - you will find that you do make substantial progress.
HTH