It sounds like you were making the best decisions you could with the knowledge you had at the time for your daughter.
If the investment bond is in your name and not in trust, I think this is very good news indeed. It's likely you may be able to access most of the fund in a lump sum by using the 5% rule without tax penalties, as follows:
Each year you can withdraw 5% of the investment without a tax liability.
As I understand it, the tax liability only kicks in if there is a chargeable event.
The 5% per year is cumulative for past years, so you can add up previous years 5% allowances by calculating the value of the fund each year for the past 18 years (SJP should do this for you as they will have the correct figures). This gives the total you can withdraw from the fund without a chargeable event. There is no time limit on the number of years you can carry forward.
www.mandg.com/wealth/adviser-services/tech-matters/investments-and-taxation/taxation-of-investment-bonds/tax-deferred-allowance-bonds#:~:text=Q.,incurring%20an%20immediate%20tax%20charge.
In your shoes, I would ask with SJP to calculate what you can withdraw under the 5% rule cumulative as a lump sum from the investment, without triggering a chargeable event. If the fund has grown on average about 5% a year I think it might add up to about £9K as a rough guide, but returns fluctuate so I might be totally off the mark.
Then either withdraw another 5% in the following tax years going forward, or in the next tax year ask SJP the tax liability of the remaining fund if you withdraw it all. As I understand it, the tax is calculated at 45% of the withdrawal, but 25% is already assumed to be paid within the investment portfolio, so a remaining 20% rate would be liable.
SJP may also have their own charges for liquidating the investment so clarify this before proceeding.
I would reiterate that an investment bond might well suit your circumstances so be sure to investigate this before deciding to ditch it. I'm not a financial adviser and I don't have a full picture. My understanding of the 5% rule is rather basic and I don't know all the nuances and pitfalls - SJP should be able to explain all your options clearly. You are paying them enough commission to expect good, reliable and concise advice on this.